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Predicted deaths from vCJD slashed

By Shaoni Bhattacharya

The worst case scenario for the deaths caused by vCJD, the human form of mad cow disease, has been revised downwards from 50,000 to 7000 by a new analysis.

In 1997, the UK research group predicted that up to 10 million people could die from the devastating disease. In 2002, the figure dropped to 50,000, based on data up to 2000. Now researchers at Imperial College, London say the likely upper limit of deaths has fallen to 7000.

Azra Ghani and colleagues used epidemiological data to model vCJD cases and deaths. Their best estimate now is that 80 more deaths will occur by 2080 – 122 have already died in the UK. However, there is still a lot of uncertainty, says Ghani.

“The large numbers [predicted] are now looking very unlikely – because you would have had to have seen an awful lot of cases by now,” Ghani told New Scientist. “But obviously 80 deaths is still 80 deaths.”

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She notes that the upper limit of 7000 was based on an analysis of data up to the end of 2001. The group has since added the data for 2002 to their analysis and submitted the results for publication. “It does look like it will be even lower [than 7,000], as we have had two years in a row now where numbers look to be declining.”

Confidence limit

Short term projections by the group also show that a dramatic increase in cases is unlikely. In the next two years, they predict 30 deaths, with upper and lower limits of 10 and 80. And in the next five years, they predict 70 deaths, with upper and lower limits of 10 and 200.

The group only looked at cases and deaths from people thought to have become infected with vCJD by eating infected meat. Their study does not account for secondary transmission of the illness, which could theoretically occur from human to human via infected surgical instruments or blood transfusions.

Ghani said a scarcity of data made it “very difficult” to say what effect this might have on a possible epidemic. Other researchers are currently examining people’s tonsils to try to determine directly the level of infection in the population.

Another factor not included in the model is the possibility that some people are more susceptible to vCJD than others. All the cases so far have occurred in people with particular versions of genes related to the prion protein that is the key to the disease. These people make up 40 per cent of the population

The remaining 60 per cent “could either be less susceptible or have a longer incubation”, says Ghani. This could at worst double the number of deaths, she says. But if incubation periods are longer, perhaps 25 years, then people are more likely to die of other causes first.

Journal reference&colon; Proceedings of the Royal Society B. (DOI 10.1098/rspb.2002.2313)